Apr 24, 2012
Greenhouse emissions must decrease by 3% a year
The Copenhagen Accord, put together at the United Nations Framework Convention on Climate Change meeting in December 2009, sets out the need to limit global warming to 2°C above pre-industrial levels, to avoid potentially dangerous climate change. Now researchers from the UK have re-assessed what this means for emission targets in 2020 and 2050.
"To keep below 2°C of global warming, with a chance of 50% or greater, requires greenhouse gas emissions – mainly carbon dioxide – to fall by 3% year-on-year, and starting at the latest, two decades ahead from now," Chris Huntingford of the Centre for Ecology and Hydrology told environmentalresearchweb. "This represents a massive challenge to society; the global economic crisis we are currently experiencing has, at most, created a temporary dip in emissions for 2010 of less than 1%."
Huntingford and colleagues from the Met Office Hadley Centre, the University of Oxford, Manchester Metropolitan University and the Committee on Climate Change discovered that the emission levels required in the policy-relevant years of 2020 and 2050 to meet the 2°C target are heavily dependent on the prescribed final-emissions floor – "the minimum emissions needed to allow society to function, so for instance burning oil in the process of harvesting crops and their delivery".
The higher the final-emissions floor, or the later the year of peak emissions, the greater the year-on-year emission cuts required, the researchers found. They believe it is important to estimate the extent to which new technology might eliminate emission floors, as "their presence significantly reduces the room for manoeuvre, even in the near term".
"We also find a strong dependence of future 'permissible' emissions on current emission levels," said Huntingford, "and whilst these contemporary values are well known in terms of barrels of oil burnt, ongoing uncertainty in land-use change and its impact on carbon dioxide levels requires better definition."
According to Huntingford, many other studies have also found that, in order to keep within the 2°C threshold, emissions must peak within the next couple of decades, followed by significant year-on-year emission reductions.
"What we set out to do, in addition, is to cover a very broad range of possible future trajectories in emissions, thus encapsulating all potential choices, and to place [it] within a full probabilistic framework," he said. "The probabilities are derived from capturing projections by all the major climate-modelling centres, [and] using this to parameterize a common 'simple' climate model, scanning across uncertainty in how the climate system functions."
There are many ways in which the analysis could be taken forward. "As always, hopefully the emerging better understanding of the climate system and its feedbacks will lead to improved projections," said Huntingford. "This, in turn, reduces uncertainty bounds on what the policy-relevant years 2020 and 2050 emissions are, to ensure no more than 2°C of warming."
The researchers also hope to engage more closely with economic and socio-economic modellers to ascertain the feasibility of different future emission pathways.
Huntingford and colleagues reported their work in Environmental Research Letters (ERL).
About the author
Liz Kalaugher is editor of environmentalresearchweb.